The present invention relates to a four-region semiconductor device (that is, a p-n-p-n or n-p-n-p device) including at least one further region, and, more particularly, to a four-region device having the capability of turning off upon application of a voltage signal to a control gate thereof.
Four-region semiconductor devices per se are well known in the art, and include, for example, thyristors or SCRs Many techniques exist for turning on a thyristor; however, fewer techniques exist for turning off a thyristor. One technique for turning off a thyristor is implemented in a gate turn-off thyristor(GTO). A GTO is a four-region device which has a control gate connected to one of the inner regions thereof, for example, the P-base region. With the connection made to the P-base region, a positive bias voltage of sufficient magnitude, applied to the GTO's control gate, serves to turn the GTO on. A negative bias voltage of sufficient magnitude applied to the GTO's control gate serves to turn off the GTO.
As will be appreciated by those skilled in the art, a turn-off current of significant magnitude must be supplied to a GTO's control gate to implement turn-off thereof. Since the energy requirement for the GTO control gate during turn-off is proportional to the turn-off current required thereby, this energy requirement is significant, or high.
A further deficiency of a GTO arises in a practical implementation thereof wherein the GTO has its control gate and cathode interdigitated to optimize its turn-off gain (that is, the ratio of turn-off control gate current to the device current). The deficiency is that the device area underneath the control gate does not substantially contribute to carrying device current. Consequently, such a GTO fails to utilize a high percentage of its semiconductor body for carrying current through the device.
Another deficiency of a GTO is that its speed of turn-off is limited by carrier recombination in the inner region of the device which is not connected to its control gate, after the p-n junction between the two inner regions of the device becomes reverse biased.